This series of patches was inspired by recent threads on the alsa mailing list, as well issues detected with existing and upcoming hardware:
1. there was a request from the PulseAudio community to get more information from drivers to make rewinds safer. While the conclusion was that it's nearly impossible for a driver developer to provide this information, there are however ways to assess the granularity of the hw_ptr updates using timestamping capabilities, and indirectly understand how safe rewinds might be.
2. There was also a request to add a start_at capability based either on system hr timers or a wall clock, which requires a means to expose both types of information to applications. Rather than adding new sets of timestamps, it is suggested the new start_at functionality relies on the new definition provides by these patches
3. For new hardware, there is a neeed to let low-level drivers handle timestamping instead of having the ALSA core do it. Similarly there is a need to let the low-level driver update the initial estimate for the trigger timestamp if there are delays to start a stream (eg. with USB)
These patches try to provide an answer to these multiple needs by building on the work done two years ago to expose wall clock information to applications. The evolution is to let application select which audio timestamp they are interested in, track the delay and drifts between recurring measurements and get, when possible, an idea of the accuracy of the underlying hardware. A backwards compatible mode is provided in case userspace doesn't provide any timestamp selection (results based on HDAudio wallclock for playback, hw_ptr in all other cases).
The first 4 patches are corrections for misses in the way the system and trigger timestamps are handled, and the last 6 provide the additional audio timestamping selection. A second batch is planned to enable hardware capabilities in a low-level drivers.
A corresponding set of patches is available for alsa-lib.
V2 changes:
trigger_tstamp: trigger_tstamp_latched, pending redefined as bool trigger_tstamp_latched reset in snd_pcm_pre_start()
audio_ts_config, report: keep separate structure but use different bitfields for in and out. use u32 instead of __u32, add comments that these structures are internal COMPAT backwards compatible mode, uses WALL_CLOCK/LINK for HDAudio playback and DEFAULT (hw_ptr) everywhere else
INFO bits: reclaimed 32-bits from hw_params, renamed as info_ext moved all timestamp info to info_ext
snd_pcm_status: read only 32-bit audio_tstamp_data, ignore all other fields
V3/4: Addressed feedback from Jaroslav: no change to STATUS ioctl, new functionality introduced in STATUS_EXT ioctl with r/w params. bumped PCM protocol for detection on STATUS_EXT in userspace used 32-bit word for accuracy report, no mantissa/exponent packing rolled back info_ext changes, all INFO fields remain in same word
Merged comments from Liam (code simplifications) fixed packing
Added driver_tstamp field in case there is a delay in passing the tstamp and audio_tstamp over IPC.
v5: no functional change, only addressed Takashi comments on patch 2,3,4 fixed used of bool with true/false and ! in comparisons move trigger_tstamp_pending_update flag to snd_usb_substream, will be used by ALSA core when other devices need it
v6: rebased on v3.19-rc7 after merge of initial 4 patches address Takashi's comments: simplified parameter handling, const and zero-clear cleanups in pcm.h, fix git-bisect issue
Pierre-Louis Bossart (7): ALSA: core: selection of audio_tstamp type and accuracy reports ALSA: core: pass audio tstamp config from userspace ALSA: core: pass audio tstamp config from userspace in compat mode ALSA: core: add .get_time_info ALSA: hda: replace .wallclock by .get_time_info ALSA: core: remove .wall_clock ALSA: bump PCM protocol to 2.0.13
Documentation/sound/alsa/timestamping.txt | 200 ++++++++++++++++++++++++++++++ include/sound/pcm.h | 66 +++++++++- include/uapi/sound/asound.h | 36 +++++- sound/core/pcm_compat.c | 28 ++++- sound/core/pcm_lib.c | 88 ++++++++----- sound/core/pcm_native.c | 41 +++++- sound/pci/hda/hda_controller.c | 40 ++++-- 7 files changed, 444 insertions(+), 55 deletions(-) create mode 100644 Documentation/sound/alsa/timestamping.txt